In fact, there are multiple powerful physics-based arguments against such high mass values in the class of jetted NLS1s. First, as argued by [1]}, if NLS1s as a class had the highest inclination correction factors and therefore much higher black hole masses, than they should show a much higher fraction of beamed systems than comparison samples of broad-line Seyfert 1s (BLS1s). However, the opposite is the case: beaming and radio loudness is systematically less frequent in NLS1s as a class, than in BLS1s. A second argument was given by [2]}. According to the theory of the blazar sequence [3]}, [4]}, [5]}, both classical blazar classes FSRQs and BL Lacs have a double-humped spectral energy distribution (SED). The first hump originates from synchrotron radiation, while the second one from inverse Compton. Essentially, the blazar sequence can be interpreted in terms of electron cooling and nuclear environments. FSRQs have a photon- and gas-rich environment, and the electron cooling process occurs efficiently via inverse Compton, in particular external Compton, where the seed photons come from the accretion disk, the torus, or the ISM. BL Lacs instead are the opposite. Their environment is photon-starved, and the only cooling mechanism is synchrotron self-Compton. The SED of \(\gamma \) -NLS1s has a very similar shape to that of FSRQs, but the total emitted power is much lower (cf Fig. 1 in [6]}). This is the case also for PKS 2004-447 [7]}. This is in agreement with the findings of [8]}, who calculated the jet power of NLS1s, FSRQs, and BL Lacs. They found that jetted NLS1s have systematically lower jet power than FSRQs, but comparable to BL Lacs. This can be interpreted in terms of mass difference since, as predicted theoretically by [9]}, the jet power scales non linearly with the black hole mass. The physics behind jetted NLS1s and FSRQs is exactly the same, hence the similar SED, but NLS1s are scaled-down versions of FSRQs because of their lower black hole mass. This result is confirmed by the observations of their radio luminosity function, that clearly showed how jetted NLS1s are the low-luminosity tail of FSRQs [10]}. Vice versa, in BL Lacs the mass is similar to FSRQs, but the cooling mechanism is different because of the different environment, and this translates into the lower jet power and the different SED. It is worth noting that, if NLS1s had high-mass black holes, they would have a low jet power in a high-density environment. This would indicate that the relativistic electrons of their jets are not cooling despite the photon-rich environment, and this is clearly unphysical [2]}. Therefore, the only reasonable explanation for the different jet power in FSRQs and NLS1s is the black hole mass, and NLS1s do not fit in the classical blazar sequence because their behavior is not regulated only by electron cooling. The blazar sequence is missing an ingredient, that is the black hole mass or, if NLS1s are the progenitors of FSRQs, the evolution of AGN [12]}.
